This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 49 673.0, filed on Oct. 14, 1999, and German Patent Application 100 03 647.3, filed on Jan. 28, 2000, the entire disclosures of which are incorporated herein by reference.
The invention relates to a boring arrangement to be connected to a boring machine equipped with a boring tool such as a bit for boring holes, especially in overlapping workpieces. The invention further relates to a method of boring holes using such a boring arrangement.
In the field of aircraft construction, the assembly of various structural components is typically carried out by boring holes in the respective components and then securing the components to each other using rivets engaged in the bored holes. To carry this out, the components are typically first laid into respective contour-determining jigs or similar apparatus. The respective joint surfaces of the components are overlapped with each other, whereby one of the workpieces has been provided with prebored pilot holes and the other workpiece is without holes. The bored holes are then formed in the overlapping joint surfaces, whereby for example the bored holes must have a critical spacing or offset away from the edge of the respective component, by means of copy-boring the pilot holes from the first workpiece onto the second workpiece that did not have any prebored holes.
For example, the fabrication of crosswise or transverse joints of an aircraft fuselage is carried out in that two large-format components are moved together so that an outer circumference of the first component is pushed over the inwardly lying transverse joint lip of the second component to form an overlap area. In order. to join this overlap area, a plurality of rivet holes or bores must be prepared. To prevent mis-alignments or improper displacements between the respective bored holes that correspond to each other in the two respective components, the pilot bores that were predrilled in the first component are directly copied by copy-boring into the second component so as to form the required rivet holes. During the progress of the copy-boring process, at least some of the completed bored holes are temporarily secured by means of temporary screw connectors.
After all the required bored holes along the respective joint surface of the components have been completed, the boring chips, turnings, and other swarf material, which arose during the boring process and which have largely collected in the overlapping joint surfaces between the two components, must be removed before carrying out the riveting. This is achieved by again separating the two components and then deburring and cleaning the joint areas. As a special further step in the assembly of an aircraft fuselage, these joint areas must additionally be provided with a sealing compound. After this step, the first and second components are once again moved together into their respective final positions with an overlapping joint area in which the respective bored holes align with one another.
Temporary holding or tacking rivets are set into about half of all of the rivet holes, and now the remaining bores or holes can be bored to the required finished dimension, countersunk, deburred on the boring bit exit side, and then the respective fitting rivets are set into these holes. Thereafter the temporary holding or tacking rivets are again removed by being bored out, and also these holes in which the temporary tacking rivets had been arranged are now bored to the finished hole dimension and further prepared for receiving respective fitting rivets therein.
Due to the great number of rivet holes that are necessary for the assembly of the fuselage of an aircraft, and especially a large commercial passenger aircraft, the above described assembly sequence is very work intensive. This. is particularly, true because the components being joined must again be separated and moved apart after the required holes have been bored therein, and then the boring swarf that has accumulated in the joint surfaces between the two components must be removed as described above, through labor intensive steps. The subsequent re-overlapping of the two components requires great care to avoid positioning errors or inaccuracies which might arise with respect to the alignment of the bored holes in the two workpieces. Considerable effort is required for removing or correcting any such positioning inaccuracies that may occur.
In view of the above it is an object of the invention to provide a boring arrangement as well as a boring method of the above mentioned general type, which can considerably reduce the assembly time and effort involved in joining together components having overlapping joint surfaces, especially with a great number of rivet holes that must be bored and rivet connections that must be set therein. Particularly, it is an object of the invention to reduce the process throughput time for the fabrication of overlapping joint surfaces on structural components, for example the transverse joint assembly of an aircraft fuselage. More particularly, the invention aims to avoid the accumulation of boring chips, cuttings, turnings, and other swarf material in the overlapping joint areas of overlapped workpieces that are being bored. It is a further aim of the invention to avoid or overcome the other disadvantages of the prior art, and to achieve further advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a boring arrangement adapted to be connected to and used together with a boring machine equipped with a boring tool such as a boring bit or drill bit, especially for boring holes in overlapping workpieces. The boring arrangement includes a first element on the boring machine side and a second element on the workpiece side. In other words, the first element is generally connected to or in contact with the boring machine, while the second element is generally in contact with the workpiece. The two elements are operatively connected and cooperate with each other so as to enable a relative motion therebetween in the boring feed advance direction. The boring arrangement further includes means for transmitting a contact force or pressing force against the workpiece. The second element on the workpiece side cooperates with a pressing sleeve that can be set onto one of the workpieces, and that has an opening such that the boring bit can be guided and moved therethrough for boring a hole into at least one of the workpieces. Moreover, the boring arrangement includes an air flow or suction arrangement for removing swarf material such as chips and dust particles from the boring site, and thereby prevents the formation of a chip jam or the accumulation of swarf in the boring arrangement as well as in the joint areas of the workpieces.
The above objects have further been achieved according to the invention in a method for boring a hole in the overlapping joint area of overlapping workpieces. A first one of the workpieces has a pilot hole that has been provided therein. In the inventive method, the pressing sleeve integrated into the boring arrangement is guided and set into the pilot hole in the first workpiece, and then held against the second workpiece with a pressing force. The boring bit is guided through the pressing sleeve and pressed against the second workpiece with a boring feed advance force so as to bore the bored hole. In this context, the machining forces and particularly the boring feed advance forces arising during the boring process are always smaller than the pressing force with which the pressing sleeve is pressed against the second workpiece. Moreover, swarf material arising during the boring process is simultaneously removed during the boring process.
According to the invention, it is especially advantageous that no boring chips, turnings, dust, fiber residues, or other swarf particles can accumulate in the joint surfaces between the two overlapping components, because the swarf materials are contained in the pressing sleeve and then suctioned away. For this reason, the overall assembly process can omit the additional steps of separating and moving apart the two workpieces, deburring the bored holes, cleaning the joint areas, moving the two workpieces once again into the overlapping position, and tack-riveting or otherwise holding the two components together after the copy-boring of the tacking holes. Thus, the total number of work steps involved in the joining operation during the structural assembly of the workpieces, and especially during the transverse seam assembly of an aircraft fuselage, can be significantly reduced. This makes it possible to achieve shorter total assembly and throughput times in the overall manufacturing of components or structures such as an aircraft fuselage.
In a particular embodiment, the boring machine side first element comprises a fixed inner sleeve, while the workpiece side second element comprises a movable outer sleeve that is connected to the inner sleeve by guide bolts so as to enable a relative sliding motion between these two elements in the boring feed advance direction. Alternatively, the first element on the boring machine side may comprise a fixed outer sleeve, which has a receiver or mount for receiving the second element which comprises a movable inner sleeve, so as to enable a relative motion therebetween in the boring feed advance direction.
The above mentioned guide bolts are preferably provided with helical compression springs thereon as a simple and economical embodiment for achieving a predeterminable pressing force and providing the required operative connection between the outer and inner sleeves that form the first element and the second element, or the second element and the first element, respectively. As an alternative, a spiral spring such as a helical compression spring may be integrated into the outer sleeve element, such that this spiral spring provides the required relative motion between the outer sleeve element and the inner sleeve element, in a space saving manner that is not sensitive to fouling or contamination.
The air flow arrangement for removing swarf material preferably includes a suction opening in the boring machine-side first element, as well as a suction pipe connected to this opening. Moreover, air holes are provided in the pressing sleeve in order. to establish the required air circulation. These air holes in the pressing sleeve may be in the form of plural holes distributed about the circumference of the pressing sleeve, whereby the holes are small enough so that no swarf material can penetrate radially out of the pressing sleeve through, these holes. Alternatively, the air holes in the pressing sleeve may be in the form of a gap or slot formed between overlapping flanks of the shell wall of the pressing sleeve, in such a direction that the air flowing inwardly through the gap travels in a direction tangent to the rotation direction of the boring bit. Additional bypass holes or bores may be provided in a conical portion of the second element in order to support the air circulation.
This arrangement creates an air circulation to achieve an axial transport of swarf material without allowing swarf chips or the like to escape radially outwardly out of the pressing sleeve. Thus, all of the swarf material is maintained inside the pressing sleeve, and is then sucked away by the suction arrangement. Directly in the area of the boring location, extending in a direction toward the suction pipe, a defined air channel may additionally by provided to have a cross-section matching the suction pipe, in order to prevent a so-called cyclone effect which would otherwise tend to reduce the air flow velocity and thereby cause the swarf material to settle out of the air flow. Thereby, an advantageous flushing air flow is maintained to flush the swarf material away from the boring location and into the suction pipe, where it is sucked away.
Regarding the combination or interaction between the boring arrangement and the boring machine, various embodiments are possible. For example, the boring arrangement may generally be arranged as an accessory on the front or working end of the boring machine, whereby the first element is secured to the boring machine via a threaded receptacle, and whereby this first element at least partially encloses and surrounds the boring bit. Alternatively, the first element may be embodied as a sleeve that is connected via a receiver or mount to the boring machine, preferably by means of a clamping screw or other fastening device that prevents a relative rotation therebetween.